1. Field of the Invention
The present invention relates to a magnetoresistive effect element (MR element) that detects magnetic field intensity as a signal from a magnetic recording medium and, especially relates to a method for producing a thin film magnetic head that has an MR element in a current perpendicular to plane (CPP) type structure (CPP-MR element), and more specifically relates to a method for producing a thin film magnetic head in which a track width having an ultra narrow size that exceeds limits of photolithography technology can be securely and constantly formed.
2. Description of Related Art
In recent years, with an increase in the high recording density of hard disk drives (HDD), there have been growing demands for improvements in the performance of thin film magnetic heads. For a thin film magnetic head, a composite type thin film magnetic head has been widely used; it has a structure where a reproducing head having a read-only magnetoresistive effect element (hereinafter, magneto-resistive (MR) element) and a recording head having a write-only induction type magnetic conversion element are laminated together.
As a reproducing head, a GMR element having a current perpendicular to plane (CPP) structure (CPP-GMR element) has been proposed. The CPP-GMR element does not includes an insulating layer between upper and lower shield layers (i.e., the upper part shield layer and the lower part shield layer) with a structure in which the upper and lower shield layers and an MR element are electrically connected in series. This technology is essential to achieve a high recording density that exceeds 200 Gbits/in2.
The CPP-GMR element has a lamination structure containing a first ferromagnetic layer and a second ferromagnetic layer formed in a manner of sandwiching a conductive nonmagnetic intermediate layer from both sides. The typical spin valve type CPP-GMR element has a lamination structure from the substrate side sequentially as follows: a lower electrode, an antiferromagnetic layer, a first ferromagnetic layer, a nonmagnetic intermediate layer, a second ferromagnetic layer and an upper electrode.
A magnetization direction of the first ferromagnetic layer, which is one of the ferromagnetic layers, is pinned in the perpendicular direction to a magnetization direction of the second ferromagnetic layer when the externally applied magnetic field is zero. The magnetization of the first ferromagnetic layer can be pinned by making an antiferromagnetic layer adjacent thereto and providing unidirectional anisotropic energy (also referred to as “exchange bias” or “coupled magnetic field”) to the first ferromagnetic layer by means of exchange-coupling between the antiferromagnetic layer and the first ferromagnetic layer. For this reason, the first ferromagnetic layer is also referred to as a magnetic pinned layer. On the other hand, the second ferromagnetic layer is referred to as a free layer. Generally, a longitudinal bias layer is located and formed on both sides of the free layer in its width direction through an insulating layer.
A tunneling magnetoresistance (TMR) element that uses a tunneling magnetoresistance effect is included in the same category as the CPP structure in view of a flowing direction of an electric current.
With an increase in the recording density, there have been growing demands for improvements in the performance of a reproducing element of a reproducing head, such as narrowing of the “read-gap length,” a gap between upper and lower shield layers, and narrowing of a track width, a width of an element. A main object of the present invention is to provide an improved technology to comply with the latter demand, narrowing of the track width. Specifically, a main object of the present invention is to provide a method for producing a thin film magnetic head in which the track width having an ultra narrow size that exceeds limits of a photolithography technology can be securely and constantly formed.